Device and method for embolus detection

ABSTRACT

A device for detecting embolus uses ultrasonic signals reflected on a fluid flow in a body. The device features a first ultrasonic unit for receiving a first signal generated in a first position in a vessel and a second ultrasonic unit for additional reception of a second signal generated in a second position in the body. The device also features a detector unit for detecting the embolus. The detector unit is triggered only if the time interval between the characteristic changes in the first and second signal, corresponding to a possible embolus, exceeds a minimum value, or if the characteristic signal change occurs in one of the signals only.

FIELD OF THE INVENTION

The present invention concerns a device for embolism detection as setforth in the classifying portion of claim 1, and a method of embolismdetection.

BACKGROUND OF THE INVENTION

Such devices and methods of the general kind set forth are used inmedical ultrasound diagnostics in order on the basis of the reflectedultrasound Doppler signals and in particular changes therein to be ableto draw conclusions about foreign bodies which are disposed in a bloodvessel. It is known that in particular embolisms or comparable foreignbodies are distinguished by a reflection characteristic in respect ofthe introduced ultrasonic signal, that is greatly different incomparison with a surrounding fluid medium—for example blood—, so thatthese particularities are used for embolism detection.

In that respect, the state of the art includes devices which, bysuitable demodulation of the received reflected Doppler signal andsubsequent acoustic output afford an operator—for example a doctordealing with the case—an acoustic way of detecting an embolism. Thelatter is expressed in the acoustic output signal by virtue of acharacteristic noise.

In addition the state of the art discloses apparatuses which alsoprepare an ultrasonic signal reflected from a flow of blood, for opticaldisplay and evaluation. Those apparatuses are distinguished in that areceived ultrasonic signal which is reflected at the flow of blood in avessel is demodulated and subsequently prepared by means of digitalimage processing in such a way that a spectral representation of theultrasonic signal (of the motion signal) in relation to time can beobtain for example on a surveillance monitor. Especially providedprocessors implement in that respect the necessary steps for imagegeneration, in particular Fourier transformation of the received data.In that way then a detected foreign body would be visually representedon the display screen, for example by virtue of coloured emphasis of thecharacteristic signal amplitude of the embolism signal in thesurrounding flow of blood in the spectral representation.

In practical operation however it has been found useful to effect thedetection of foreign bodies in the blood stream in a more precise mannerand in particular also to make it possible to distinguish embolisms fromso-called artefacts, more specifically signal disturbances of anultrasonic probe which is used for the methods and devices of thegeneral kind set forth—as occur for example due to movements of theprobe; more specifically, just like an embolism, an artefact results ina characteristic signal change in an optical or acoustic output signalof the device and, in the case of an artefact, would impair diagnosticaccuracy and result in the operator being unnecessarily distracted.

The specific task of distinguishing an embolism or the like foreign bodyin the bloodstream from an artefact was approached in various ways inthe state of the art. Thus for example the teaching of U.S. Pat. No.5,103,827 makes use of the properties of an artefact (in comparison withan embolism) that, in the case of an artefact, the image representationor display involves a bi-directional spectral signal (both in a positiveand also a negative direction) which can be distinguished from auni-directional embolism signal by virtue of suitable circuitry measuresand measures relating to signal processing procedures. However such asolution, due to the necessary variable thresholds for distinctionpurposes and the complication and expenditure which this entails, isonly limitedly suitable for affording a simple and convenient way ofdistinguishing embolisms. In addition it is precisely in relation torelatively large embolisms that the problem arises that—for example dueto over-driving of interposed amplifier units—such relatively largeembolisms also result in a bi-directional spectral representation sothat in that respect the path adopted cannot in any case lead to asatisfactory result.

In addition U.S. Pat. No. 5,348,015 describes a further approach fordistinguishing an artefact from an embolism. In particular the inventorshere propose using a multi-channel device which is operated at variousfrequencies for embolism detection and distinction. As more specificallythe ultrasonic reflection properties in particular of an embolism arefrequency-dependent, that affords a secure way of distinguishing samefor example from an artefact (which is uninfluenced thereby). Morespecifically, in the case of an embolism—in contrast to an artefact—asignal (amplitude) strength which is different for various ultrasonicfrequencies is to be established in the spectral representation, andthat strength can then be evaluated. It will be noted however that thedevice described in U.S. Pat. No. 5,348,015 is extremely complicated andexpensive and, besides a plurality of transmitting and receivingchannels (that is to say signal generation, reception and demodulationare respectively required separately), the device also requires specialprobes which are suitable for a multi-frequency mode of operation, andin addition it gives rise to considerable difficulties in regard tocontrol and software engineering. In particular from the point of viewof inexpensive and uncomplicated implementation of reliable embolismdetection and distinction therefore, this approach also appears tosuffer from disadvantages.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore that of improving adevice for embolism detection of the general kind set forth, in such away that detection of an embolism and in particular distinction thereoffrom an artefact can be effected in a more reliable and simpler fashion.The invention also aims to provide a suitable embolism detection method.

That object is attained by the device having features of claim 1 and themethod as set forth in claim 9.

The device according to the invention advantageously makes it possibleto reliably distinguish an embolism from an artefact on the basis of twosignals which are evaluated in respect of their respective signalchanges—which could indicate an embolism—and the time interval betweenthose signal changes.

In that respect the invention makes use of the principle that anartefact, produced for example by movement of the ultrasonic probe inthe position of attachment to the head and as an interference signal inthe two signals to be evaluated occurs substantially simultaneously orhowever only with a minimum time interval. In comparison an embolism ismade distinguishable by virtue of the fact that, when reaching the firstposition in the (blood) vessel, it produces the characteristic signalchange for example arise in amplitude—while this still cannot be thecase at the second position which is different from the first position,at that moment in time. On the contrary, at the second position, if thisis also in the same vessel, the characteristic signal change occurs inrespect of time prior to or after the first signal change, in dependenceon how the first and second positions are arranged relative to eachother in the direction of flow of the fluid (the embolism moves with thespeed of flow of the fluid in the vessel) so that the time intervalbetween the respective signal changes corresponds to the duration oftransportation between the two positions. If the second position isarranged outside the vessel, then in the normal case no characteristicsignal change in the second signal is produced by the embolism in thevessel.

In that respect, in connection with the invention, the ultrasonictransmitting device may have one or a plurality of ultrasonic probes.

Advantageous developments of the invention are set forth in theappendant claims.

Thus it is particularly preferred for the second position to be arrangedoutside the vessel to be monitored; in a further preferred feature thatposition—when implementing monitoring on the head of a patient—is at adepth of between about 30 and about 35 mm in relation to the surface ofthe head and directed onto a skull bone.

In that way there is then practically no change in the secondsignal—that is to say in the reference channel—when an embolism passesthe first position and thereupon the first characteristic signal isgenerated.

It is also to be assumed that the minimum time interval in use in apractical medical context is practically zero and even theoreticallydoes not exceed between 2 and 3 msec.

Advantageously there is provided a so-called gating system for embolismdetection according to the invention, more specifically evaluation,displaced in respect of time, of the same reflected transmitting signal,whereby observation of two different depths of penetration in the bodyis made possible. In accordance with the invention a first depth ofpenetration is set to the first position while preferably the depth ofpenetration which determines the second position is outside the vessel.It is also in accordance with the invention to provide a plurality ofgates—which are for example graduated or stepped in terms of the depthof penetration—and of which then at least one is to be used as areference gate to be employed to generate the second signal.

While moreover operation of the detector unit is usually implemented onthe basis of first and/or second signals which are transformed into thetime domain (that is to say FFT), embolism detection and distinction isin principle also possible in the time domain in accordance with theinvention; it is advantageously possible in that way to save on anFFT-processor at least for the reference channel.

Further advantages, features and details of the invention will beapparent from the description hereinafter of specific embodiments andwith reference to the drawings in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a block circuit diagram of the device according to theinvention for embolism detection in accordance with a first embodimentwith two mutually independent probe units,

FIG. 2 shows an alternative embodiment of the invention with anindividual probe unit, for which there is provided a reference gate,

FIG. 3 shows a block circuit diagram of a further embodiment of theinvention which provides a multi-gate system with up to four probes andup to eight gates which are to be associated in any desired manner withthe probes, at least one of said gates serving as a reference gate forembolism distinction, and

FIG. 4 shows a signal diagram with a representation of three signalconfigurations in relation to time for embolism distinction.

DETAILED DESCRIPTION OF THE INVENTION

The block circuit diagram in FIG. 1 shows the detection part of a devicefor embolism detection in accordance with a first preferred embodimentof the invention (best mode). The arrangement has two mutuallyindependent probe channels (indicated in the Figure by the indices “a”for the first channel and “b” for the second channel) which respectivelygenerate separately in themselves an evaluatable ultrasonic Dopplerreception signal, which is then used in the procedure according to theinvention for embolism detection or distinction.

A first probe 10 a is connected on the transmitting side to a firstmultiplexing and transmitting unit 12 a which is designed for currentfrequencies of ultrasonic sonography, for example 2, 4, 8 or 16 MHz, andwhich is connected to an oscillator module 14 a disposed upstreamthereof.

On the receiving side an output signal of the first probe 10 a isapplied to a first multiplexing and pre-amplifier unit 16 a, issubsequently processed by a first mixer and demodulator unit 18 a, andis passed to a first (programmable) high pass filter 20 a. In thearrangement shown in the block circuit diagram, the filter 20 a isfollowed by a first adjustable amplifier 22 a (“programmable gain”)whose output signal is processed by a first sample-and-hold (S & H)circuit 24 a.

The signal produced in that way is then applied on the one hand to afirst audio filter 26 a for signal output for an embolism signal whichis to be acoustically evaluated, and on the other hand a commonFFT-processing unit 28 (FFT=Fast Fourier Transformation) receives theoutput signal of the first sample-and-hold circuit 24 a for processingof the visual representation of the Doppler signal as a spectralrepresentation in relation to time. The FFT-processing unit 28 has acommon detector unit 30 connected downstream thereof.

The parallel second channel which is connected to the second probe 10 bis of a structure corresponding to the above-described first channel,more specifically by means of a second transmitting unit 12 b which isalso controlled by the oscillator 14, and on the receiving side by meansof multiplexer/pre-amplifier unit 16 b, mixer 18 b, high pass filter 20b, amplifier 22 b and sample-and-hold circuit 24 b whose signal is againpassed on the one hand to a second audio filter 26 b and on the otherhand is also applied to the common FFT-processing unit 28.

A common control unit 32 which is implemented by means of amicrocontroller provides on the one hand for control of the first andsecond high pass filters 20 a, 20 b, the first and second intermediateamplifiers 22 a, 22 b and the two sample-and-hold circuits 24 a, 24 band in addition provides for control of the oscillator unit 14. Thelatter in turn controls the mixer units 18 a, 18 b provided forquadrature demodulation. In addition, associated with each probe 10 a,10 b is an identification signal line 34 a, 34 b for the control unit32.

With the exception of the common FFT-processing unit 28 and the detectorunit 30, the circuit which has been described hereinbefore is a currentproduct, as is offered by the applicants for example under the name“Multi-Dopp” as a two-channel system for medical ultrasonic diagnostics.

In a manner which is advantageous in accordance with the inventionhowever, the invention provides that drawing a distinction between anembolism and an interference signal to be suppressed, for example anartefact, is effected in the detector unit 30, by evaluation of arespective reception signal—in the illustrated embodiment, after aFourier transformation operation, that is to say in relation to a signalin the frequency region.

In the manner which is advantageous according to the invention, thedetector unit 30 is designed as an electronic unit for digital signalprocessing, in such a way that an artefact which is expressed in bothchannels as a substantially simultaneous, marked rise in amplitude ofthe reception signal, is recognised as such by virtue of therelationship in respect of time between the channels and consequently noembolism detection signal is outputted on a detector signal output 36.

To put this more precisely, for example a movement of the probes whichcan be secured by means of a suitable support unit to the human body,for example on the head, results in an unwanted, high-level receptionsignal, caused by such movement, in both probes, occurring practicallysimultaneously (or within a time interval of less than 3 ms). Thereception signal in both channels, which is further processed inaccordance with the processing units in the block circuit diagram ofFIG. 1, is then to be identified as simultaneous by the common detectorunit, whereupon then the conclusion is drawn that an artefact isinvolved. In comparison for example the occurrence of an embolism in adetection region of the first probe (which is suitably directed forexample onto a region of a blood vessel) would result in a (high-level)signal while the second probe which is directed onto another region ofthe blood vessel, onto a region of tissue or bone outside or howeveronto another vessel (or which for example in the case of measurement onthe head is disposed on the opposite end) would not detect the embolismdetected in the first channel. For that reason, a detection signal ofhigh amplitude admittedly occurs in the first channel but not in thesecond channel (or, in the case of spatial displacement of the twodetection regions of the probes in the same vessel, at a time intervalcorresponding to the transportation speed in the flow of blood). In acorresponding manner it is possible by means of the detector unit toestablish that a characteristic rise in signal has not occurred at thesame moment in time in both channels so that it is possible to concludethat an embolism is involved.

As FIG. 1 shows FFT-outputs 38 a, 38 b are provided for subsequentvisual signal representation of the transformed signals of the signalchannels which are designed in the known and usual manner, and inaddition an operator handling the device can acoustically monitor therespective channel by way of audio outputs 40 a, 40 b of the first andsecond audio filters 26 a, 26 b respectively.

An additional gate and multiplexer unit 42 which is shown in broken lineand which is connected downstream of the second pre-amplifier unit 16 bimplements a development of the embodiment shown n FIG. 1: morespecifically, the additional unit 42, as indicated by the further lineshown in broken form, also receives the output signal of the firstpre-amplifier 16 a, triggering the function of the gate and multiplexerunit 42. In accordance with the output signal of the first pre-amplifier16 a, the unit 42 produces a certain time delay in regard to samplingfor the second channel (b) whereby—due to the different transittime—another detection region (more precisely: another detection depth)is afforded for signal preparation in the second channel. The referencesignal formed in that way (considered as the “gate” in accordance withthe time displacement) is then, in the described manner, along thesecond channel, mixed and demodulated (18 b), filtered (20 b), amplified(22 b) and sampled (24 b) so that the output signal of the probe 1occurs at the common FFT-processing unit in duplicate—produced on theone hand by the first channel and on the other hand produced by thesecond channel, displaced by the gate spacing.

The output signal of the second channel therefore corresponds to adisplacement in respect of location of the detection depth with respectto the first channel, wherein that displacement—depending on therespective setting of the multiplexer/gate unit 42—can lead or trail thefirst channel, in regard to a depth of penetration. In particular thegate provided in that way can also be set in such a fashion that the(reference) gate signal produced by means of the multiplexer/gate unit42 does not fall into the vessel which is being monitored in the firstchannel, but for example on a bone or a piece of tissue adjacent to thevessel. In that case no high-level detection signal will be outputted inthe second channel which is additionally used as a reference, if anembolism in the blood vessel produces a signal change in the firstchannel, so that then the existence of an embolism can becorrespondingly reliably established.

FIG. 4 shows a usual transit time or depth setting which is suitable inparticular also for operation of the device shown in FIG. 1. While boththe detection region for the first channel a (uppermost signal in FIG.4) and also for the second channel b (second signal in FIG. 4) are putto a depth of between about 40 and 45 mm from the probe surface—in theillustrated embodiment measurement is effected by way of the channels aand b on both sides of the head—the reference signal in the firstchannel a_(REF) is put to a depth region of between 30 and 35 mm, whencarrying out measurements on the head near the skull bone of the patientand in dependence on the respective anatomy involved. As the trigger orclock signals in FIG. 4 show therefore in the case of an embolism—whichwould not be detected in the reference gate as with positioning on thebone the latter is outside the vessel—only the first channel wouldgenerate an embolism detection signal but the reference channel and thesecond channel would not. In comparison an artefact would occur equallyin the signal channel a and in the reference channel a_(REF). The gatetherefore produces a delay corresponding to a depth of penetration,which is different in relation to the signal channel, due to the varyingtransit time.

FIG. 2 illustrates a block circuit diagram showing a simplifiedembodiment which is slightly modified in relation to the embodiment ofFIG. 1. Corresponding functional elements are denoted by referencescorresponding to those used in FIG. 2, FIG. 2 having a first completesignal channel which at the end in turn has an FFT-output 38 and anaudio output 40 while the reference gate is not in the form of acomplete signal channel but only in the form of a mixer/gate unitconnected downstream of the pre-amplifier 16, corresponding to the unit42 in FIG. 1. This simplified Doppler channel does not require thefurther, downstream-disposed signal preparation operation for it is onlyrequired for detection and distinction of an artefact (and not forexample for further calculation and representation of aFourier-transformed spectral imaging).

Accordingly the detector module 44 detects both the reception signal ofthe first channel and also the signal of the reference channel, which isoutputted by the gate unit 42, and produces therefrom a detector outputsignal for the detector signal output 36 when in the above-describedmanner a characteristic amplitude signal occurs at the output of thesample-and-hold circuit 24, but a corresponding signal does not occur atthe same moment in time at the output of the reference gate 42.

FIG. 3 shows a further embodiment of the present invention, morespecifically in the device shown in FIG. 3 a total of up to fourdifferent probes 10 a through 10 d (corresponding to a respective one offour channels a, b, c, d) can be connected, which at the transmittingside are acted upon by transmitting units 12 a through 12 d and which onthe receiving side are tapped off by pre-amplifiers 16 a through 16 dwith mixer/demodulator units 18 a through 18 d connected on the outputside thereof. Connected downstream of the mixer units as a multiplexarrangement are eight gate channels each comprising a controllablegates, a high pass HP_(i) and a sample-and-hold circuit S&H_(i) (in eachcase i=1 . . . 8). Control and variable, individually settableassociation of the respective gate channels with the four probe channelsis implemented by the action of a gate control unit 46 which is in theform of a suitably designed controller. That control unit which has anoscillator portion also controls the transmitting units and thereceiving units which are connected upstream of the gate units; themultiplex audio output, comprising audio multiplexer 48, equalizer 50and audio processor 52, as well as an FFT-processing unit 54 for furtherprocessing and output of the signals for visual representation aresupplied with control signals by the control unit 46.

Connected downstream of the FFT-processing unit 54 once again is anembolism detector unit 56 having a detector signal output 36 which inthe above-described manner, from the FFT-transformed gate signals whichoccur in the form of a multiplex signal, evaluates at least one of theeight gates as a reference gate and from the signal configurationsconcludes the occurrence of an embolism (as distinct from an artefact).

The embodiment illustrated in FIG. 3 permits in a highly flexible mannerthe use of up to four different probes, wherein, similarly to the modeof operation as described with reference to FIG. 1 or FIG. 2, a singleprobe also already permits complete embolism detection operation inaccordance with the present invention, as long as at least one of theeight gate channels is set up in the above-described manner as areference channel and in particular is directed onto a differing(reference) detection region outside a vessel to be monitored. Theremaining gates can then monitor for example in graduated or staggeredfashion different depths of a vessel. Alternatively, it would bepossible to envisage a configuration in which there are provided forexample two probes each with four gates which are stepped in respect ofdepth, wherein in each case at least one of the four gates is set as areference gate.

The detector unit 56 diagrammatically illustrated in FIG. 3 is thenappropriately suitably set or programmed for signal evaluation purposes.

It will be seen from the foregoing discussion that the invention can becarried into effect in various ways, in which respect in particular itis also not necessary that an FFT-transformation procedure or the likeoperation always has to be effected with the received ultrasonic signal,prior to detection of an embolism (linked to distinguishing it from anartefact, in accordance with the invention). On the contrary it iscertainly possible, see for example the original embodiment of FIG. 1,to implement that distinguishing operation solely in the time domain orregion of the signals which are detected or which are to be compared. Acorresponding consideration applies in regard to the provision ofreference gates which, by virtue of the change in accordance with theinvention in the detection time of the reflected signal, reflect thestate of a detection region in the body, which is a different region(due to the transit time involved). It is assumed that the bestdistinction between embolism and artefact, in accordance with theinvention, is possible when the detection region for the additionalreference channel is set at a location outside the blood vessel to beobserved, because in that way mutual influencing of the channels issubstantially avoided. In the above-indicated fashion however it is inprinciple also possible to provide for detecting and distinguishing anembolism if the signals to be evaluated represent two differentdetection locations in the same vessel.

All in all therefore embolisms can thus be reliably distinguished fromartefacts in the described fashion, in which respect laboratory testshave shown that—compared to known methods of embolism detection—markedlyimproved success rates can be achieved.

If the detection region for the reference channel is set to a locationoutside the vessel to be observed, then in the case of an actualembolism in the vessel there is practically no signal input into thesecond (reference) channel; any coupling or cross-talk effects areexpressed at best in only slightly rising amplitudes in the referencechannel.

Checking using measurement procedures has also shown that an artefactalways occurs practically simultaneously in both channels and leadsthere in measurable signal changes; at the longest, a time delay betweenthe channels is up to three ms, and is therefore markedly below the timesettings which are used by way of example in accordance with the presentinvention.

What is claimed is:
 1. A device for embolus detection by means ofultrasonic signals which are reflected at a flow of fluid in a body,comprising: an ultrasonic unit which is adapted for periodicallyproducing ultrasonic monitoring signals for a suitably designedultrasonic transmitting device and for receiving a first signalreflected at a first position corresponding to the flow of fluid in avessel; a signal evaluation unit which is connected downstream of theultrasonic unit for preparing and visually and/or acoustically providingthe reflected first signal; a detector unit which co-operates with thesignal evaluation unit and which is adapted to detect an embolus in theflow of fluid and to output a detection signal as a reaction thereto;wherein the ultrasonic unit is designed for additionally receiving asecond signal from the ultrasonic transmitting device, which isreflected at a second position in the body that lies outside the vesseland the flow fluid; and the detector unit is designed to detect anembolus as a reaction to the first and the second signal in such a waythat output of the detection signal occurs only if a characteristicsignal change, corresponding to a possible embolus, in one of the firstand second signals occurs outside a minimum time interval from a signalchange in the respective other signal, or the characteristic signalchange occurs in only one of the signals.
 2. The device set forth inclaim 1 wherein the minimum time interval is three msec.
 3. The deviceset forth in claim 1 wherein the ultrasonic unit is so adapted that thesecond signal is generated at a moment in time which is different fromthe first signal in accordance with a different depth of penetration ofthe ultrasonic signal into the body, from a common transmission signal.4. The device set forth in claim 1 wherein the first signal is producedfrom a first ultrasonic probe unit as a signal source and the secondsignal is produced from a second ultrasonic probe unit as a furthersignal source.
 5. The device set forth in claim 1 wherein the ultrasonicunit is so adapted that the second position is in the head region and ata depth, relative to an associated ultrasonic transducer, of betweenabout 30 and 35 mm, and the first position is at a depth of greater than40 mm.
 6. The device set forth in claim 1 wherein the ultrasonic unit onthe receiving side is of a multi-channel configuration with a pluralityof receiving units which are adapted to output discrete signal states ofthe first and/or the second signal and which can be controlled intime-displaced relationship as a reaction to a common transmissionsignal.
 7. The device set forth in claim 1 wherein the detector unitimplements processing of the first and the second signals for detectingthe embolus in the time domain.
 8. The device set forth in claim 1wherein the detector unit is so adapted that processing of the first andthe second signals for detecting the embolus is effected on the basis ofat least one signal which is transformed into the frequency domain.
 9. Amethod of embolus detection by way of ultrasonic signals which arereflected at a flow of fluid in a body, comprising the following steps:periodically emitting ultrasonic vessel monitoring signals by way of asuitably adapted probe; receiving and preparing the signals reflected ata flow of fluid in a vessel to be observed, and evaluating the preparedsignals and outputting a detection signal for a detected embolus as areaction to the received signals; additionally receiving a referencesignal which is reflected at a position in the body outside the vesselto be observed; and comparing the reference signal to the signalsreflected at the flow of fluid and determining an embolus as a reactionto the existence of a characteristic signal change, corresponding to anembolus, in the reference signal and/or as a reaction to a time intervalbetween the characteristic signal change in the reference signal and acorresponding signal change in the signals reflected at the flow offluid.